Stroke Risk Can Be Reduced Say Experts

New York(May 23, 2011)

A stroke may hit like a bolt from the blue, but the underlying cause for most strokes – damaged or blocked blood vessels in the neck or brain – begins to evolve months and years beforehand. In an ischemic stroke, by far the most common kind of stroke, an artery narrowed by a process called atherosclerosis blocks blood flow to a part of the brain supplied by that vesel; in a hemorrhagic stroke (hematoma) a blood vessel in the brain ruptures, causing damage to the brain as blood bursts into that area. In both cases the brain's supply of oxygen-rich blood is cut off and brain cells die. As many as 80 percent of the 750,000 strokes that occur in the U.S. each year could be prevented, according to the National Stroke Association, if patients and their doctors recognized and treated the controllable risk factors for stroke: high blood pressure, smoking, diabetes, abnormal cholesterol, obesity, and obstructive sleep apnea.

In people with hypertension, or high blood pressure, extra stress on the blood vessel linings causes them to thicken and deteriorate over time, said neurologist Randolph S. Marshall, M.D., Chief of the Stroke Division at NewYork-Presbyterian/Columbia University Medical Center. "The more wear and tear on the inner lining, the more likely people are to develop atherosclerosis." High blood pressure is also the cause of many hemorrhagic strokes, as it can lead to the rupture of tiny arteries deep in the brain. Dr. Marshall recommends that doctors treat hypertension with one of the many blood pressure medications now available.

Smoking is another central risk factor for stroke, Dr. Marshall said. "Many substances in cigarette smoke are directly toxic to blood vessels and damage vessel walls, setting the stage for blockages," he said. "Smokers have a more than two-fold risk of stroke, so smoking cessation is a very important step in preventing stroke."

Randolph S. Marshall,M.D.

People with diabetes have high levels of glucose circulating in the blood, which damages blood vessels walls: People with diabetes are four times as likely to have a stroke as those without the disease. Many people with diabetes also have high blood pressure and abnormal cholesterol levels, so their risk of stroke is compounded. Good diabetic control can lower their risk of stroke, according to some studies, said Dr. Marshall.

Cholesterol also plays a role in stroke, as cholesterol can accumulate in and narrow arteries. High levels of high-density lipoproteins (HDL) may reduce stroke risk, and these levels can be increased through exercise. Low-density lipoproteins (LDL) can cause the build-up of plaque. "Reducing fatty food intake will help lower LDL levels," said Dr. Marshall.

With overweight patients, doctors consider a patient's "truncal obesity," the amount of fat stored in the abdomen, to determine his or her risk of stroke. Rising rates of obesity in younger people are a significant and dangerous problem, said Dr. Marshall. "Those growing up obese are also more likely to have high blood pressure and diabetes, so stroke risk is already present and waiting to be a factor in younger people," he said.

Alan Z. Segal, M.D.

One common thread to controlling almost all of these stroke risk factors is exercise, according to Dr. Marshall, who recommends that patients follow American Heart Assocation guidelines and exercise 20 to 30 minutes most days of the week.

Researchers continue to refine their understanding of stroke risk. A recently identified risk factor is obstructive sleep apnea (OSA), said Alan Z. Segal, M.D., a neurologist at NewYork-Presbyterian/Weill Cornell Medical Center. Stroke risk is two-fold higher in people with OSA, a 2005 study showed (NEJM 2005 Vol 353 p 2034). "People with OSA may have a choking, gasping feeling on waking and may not realize why they are waking up. They also have low oxygen saturation, which is thought to promote hypertension, another risk factor. Having multiple factors obviously compounds the risk of stroke," Dr. Segal said. Doctors at NewYork-Presbyterian/Weill Cornell are now sending patients suspected of having OSA to their Sleep Center for studies, he said.

In people who have already had a stroke the risk of a second one is much higher. "For most of these patients we prescribe anti-platelet agents such as daily aspirin," Dr. Marshall said. "It turns out that aspirin also works to prevent first-time stroke for women."

NewYork-Presbyterian researchers are participating in a number of studies to help prevent stroke, including the use of intra-cranial stenting, the insertion of a short mesh tube that supports the artery walls and stops them from narrowing, as a stroke prevention approach in patients who have had a stroke or transient ischemic attack. "This is an important study of a new, secondary stroke prevention approach, which may be used in addition to medications such as anti-platelets and statins," said Dr. Segal.

Stroke is also more common among minority populations, blacks and Hispanics, who tend to have more of the risk factors outlined above, said Dr. Marshall. Researchers at Columbia's Community Resources Center in upper Manhattan are educating neighborhood residents about stroke risk and screening them as well. The co-director of the Center, Dr. Bernadette Boden-Albala, recently concluded a study in which they spent time with stroke patients and their family members, teaching them about the importance of getting to the hospital as quickly as possible when stroke symptoms appear. Those who participated in the study came to the emergency room five hours earlier than those who did not, said Dr. Marshall. "That makes a huge difference. Those who came in early were able to get tissue plasminogen activator (tPA)," a clot-busting drug that reduces the effects of stroke and the likelihood of permanent disability if given within the first three hours after stroke symptoms appear. Continued education of patients and physicians is a crucial part of the effort to reduce stroke risk.

Contributing faculty for this article:

Randolph S. Marshall, M.D. is the Chief of the Stroke Division at NewYork-Presbyterian/Columbia University Medical Center and a Professor of Clinical Neurology at Columbia University College of Physicians and Surgeons.